1. Field of the Invention
The present invention relates to bicycles specially designed for physically disabled riders, and more particularly to lever driven bicycles having simple shifting mechanisms for controlling the drive ratio between the lever and a drive wheel.
2. Description of Related Art
Typical bicycles are driven by crank systems which utilize unidirectional rotational movement to propel the bicycle drive wheel. Such unidirectional rotational movement results in a varying torque from zero, to a maximum, and back again to zero, for each half revolution. This motion is necessitated by the conventional crank design which includes a continuous chain that is received about a crank and a sprocket. Conventional bicycles also include shifting mechanisms which adjust the drive ratio between the crank and sprocket by controllably locating the chain about selected sprockets of different diameter.
These conventional crank driven bicycles with their varying torque are difficult or impossible to ride for those with certain physical disabilities, such as an amputee with only one leg, a person having one leg weaker than another, or possibly even a paraplegic who only has the use of his or her arms.
One possible solution to assist the physically disabled in riding a bicycle includes the design of a lever driven bicycle. Various lever driven bicycles have been designed which replace the conventional rotational drive with the oscillating displacement of a lever. Such lever driven bicycles utilize a dual lever arrangement in with each lever is oscillated individually by each leg of the rider. An example of this type of lever driven bicycle can be found in U.S. Pat. No. 3,039,790 to Trott. Lever driven bicycles have also been designed with shifting mechanisms which allow for manual control of the drive ratio between the lever and the drive wheel. In particular, U.S. Pat. No. 3,834,733 to Harris and U.S. Pat. No. 4,421,334 to Efros both disclose lever driven bicycles having shifting arrangements which allow the rider to manually adjust the drive ratio between the lever and drive wheel.
While the oscillating motion of the lever driven bicycle is more preferable for the physically disabled rider because of its substantially constant torque and less cumbersome linear movement, the lever driven bicycles to date still do not produce the efficient drive and ease of power application required by many persons with physical disabilities.
In light of the foregoing, there is a need for an improved lever driven bicycle which is uniquely designed to address the needs of the physically disabled.